Top Voted Answer

other obsidians close by are interfering with the portalMake sure to build only 1 layer of obsidian {}{}{}{}{}{}{}{}{}{}{}{}{}{}----{}{}{}{}----{}{} = NO{}{}----{}{}{}{}{}{}{}{}{}{}{}{}{}{}

{}{}{}{}{}----{}{}----{} = YES{}----{}{}{}{}{}

and some people forget to use flint and steel to activate the portal, they thought making the frame will activate automatically, when you actually need flint and steel and set the middle on fire, and the portal will activate

Answers

There are two possibilities: number one is as Gabain1993 stated, your portal may not be correctly made. Make it like this, one set of brackets representing one block of obsidian{}{}{}{}{} {}{} {}{} {}{}{}{}{}

Your other but less likely problem is your client has not been updated, and therfore the portal would not work